1. The Field of the Invention
The present invention relates generally to visual display devices, and more particularly, but not necessarily entirely, to visual display devices containing light modulating devices.
2. Description of Background Art
Dynamic video displays are becoming ubiquitous in modern society. Such video displays are used to display information in a wide variety of settings providing, inter alia, education and entertainment. There have been several recent promised enhancements to dynamic video display technologies including: increased resolution, increased contrast, increased brightness levels, reduced “screen door” effects as well as other characteristics which improve the overall quality of images produced with dynamic video display systems.
Technologies used to produce dynamic video displays include: Texas Instruments' DLP® projector using a digital micromirror device (“DMD”), Sony's SXRD® and JVC's D-ILA® which incorporate liquid crystal on silicon (“LCOS”) technology, Kodak's grating electromechanical system (“GEMS”) as well as systems using grating light valve (“GLV”) technology. All of these particular technologies differ in the devices which are used to modulate the light which is projected, and such modulation devices are the core of each system and the component to which the rest of the system components surrounding them are designed.
In DMD based projectors, an image is created by microscopic mirrors laid out in a two-dimensional matrix on a semiconductor chip. Each mirror represents one pixel in a frame of the projected image. The number of mirrors corresponds to the resolution of the projected image, i.e., 800×600, 1024×768, 1280×720 and 1920×1080 (HDTV) matrices are some common DMD resolutions. Each mirror can be tilted rapidly to reflect light either through the lens or onto a heatsink also called a light dump.
In DMD based projectors, the rapid tilting of the mirrors (essentially switching between “on” and “off” states) allows the DMD to vary the intensity of the light being reflected out through the lens, using pulse width modulation to create shades of grey in addition to white (white being projected in “on” position) and black (being projected in the “off” position). Disadvantageously, DMD based projectors are susceptible to a “screen door” effect which is commonly described as viewing an image through a screen door. The undesirable effect is due to the fact that the individual micro-mirrors have gaps between them. These gaps between the micro-mirrors cause gaps between the displayed pixels to become more visible as the individual/viewer comes closer to the displayed image and as the displayed pixels become larger.
In one previously available projection system, only a single DMD chip is utilized. Colors are produced by placing a spinning color wheel in the optical path between a lamp and the DMD chip. The color wheel may be divided up into three or more color filters, namely, red, green and blue. The DMD chip is synchronized with the rotating motion of the color wheel so that the red component is projected onto the DMD when the red filter is in front of the lamp. The same is true for the operation of the green and blue filters. The red, green and blue images are thus displayed frame sequentially at a sufficiently high rate that the observer sees a full color image. It will thus be appreciated that while the red, green and blue light components are temporally spaced from each other in a single DMD based system due to the use of the color wheel, that the red, green and blue light components are not spatially separated on the DMD chip. That is, each red, green and blue component of light is incident upon all of the mirrors of a DMD chip but at separate times due to the use of the color wheel.
The GEMS and the GLV technologies are similar to each other in respect that they both consist of tiny silicon-ribbons that diffract light into multiple orders. GLV technology uses two or more ribbons to form a pixel as a very finely focused column of light that is shined vertically across these ribbons. The vertically diffracted orders of light are gathered, scanned and sent through an imaging lens and thereafter they appear on a screen. Exemplary GLV based light modulation devices are described in U.S. Pat. Nos. 5,311,360 and 5,841,579, which are both incorporated herein by reference in their entireties.
In the previously available GLV based systems, three separate GLV chips, one each for red, green, and blue light sources, are utilized to form images by superimposing the colors. One such exemplary system is described in U.S. Pat. No. 6,692,129, which is hereby incorporated by reference in its entirety.
GEMS technology is similar to GLV technology except the silicon ribbons used are much longer and are suspended between multiple posts and light is diffracted horizontally (parallel to the ribbons), whereas the GLV ribbons are typically only suspended between two support posts and light is diffracted vertically (perpendicular to the ribbons). In the previously available GEMS based systems, three separate GEMS chips, one each for red, green and blue light sources, are utilized to form images.
Imaging systems using LCOS technology essentially combine the “transmissive technology” used in a liquid crystal display (“LCD”), where light is modulated by liquid crystals as it passes through various layers of materials—some of which are polarized—on its way to a lens, and the “reflective technology” used in DMD based systems where light is reflected in an “on” and “off” manner. Essentially LCOS systems are a reflective technology that uses liquid crystals instead of mirrors wherein these liquid crystals are applied to a reflective substrate. As these liquid crystals “open” and “close,” light is reflected from the reflective substrate below. LCOS-based projection systems typically use three LCOS chips, one each to modulate light in the red, green and blue channels. In this respect it is similar to an LCD-based projector which uses three LCD panels. Because they cannot operate fast enough when operating in a sequential fashion, both LCOS and LCD projectors deliver the red, green and blue components of light to the screen simultaneously. Since LCOS and LCD chips cannot operate fast enough, there is no spinning color wheel used in these projectors as there is in single-chip DMD based projectors.
Thus, typical GLV, LCOS, and GEMS based projectors will use three modulators, such modulators customarily being referred to as “chips,” to modulate light in the red, green and blue channels, which are combined to deliver light simultaneously to a screen. This arrangement is similar to LCD projectors which uses three LCD panels.
As explained above, typical DMD based systems often differ in that a single-chip modulator is used with a color wheel, which delivers red, green and blue light to the single-chip and then to a screen in a color sequential manner. This DMD technology is susceptible to color separation, also known as the rainbow effect, where light or white images that are in motion on a dark background appear to have a rainbow or shadow of colors following the image. This rainbow effect is partially caused by the fact that a DMD based system use field sequential imaging. While a single-chip DMD modulator has the mentioned disadvantages, the advantages of using a single-chip modulator are lighter and smaller packaging, fewer components and circuitry, and reduced cost.
DMD based systems have made improvements to its color rendition by sometimes adding an additional set of red, green and blue filters to its color wheel and improving the rotational speed of the wheel to help reduce the visible effects of color separation to some of the population viewing the image, however, it does not eliminate the problem altogether. In the past, other technologies, e.g., LCD, LCOS, GEMS and GLV, avoided the problem of color separation by using three separate modulators, one for each color, so the entire image being displayed from frame to frame was not separated color sequentially as with a color wheel. All three colors can be in the “on” position at the same time producing a white pixel. When white or light pixels are being displayed on a dark or black background color separation is minimized or does not occur.
In addition to color separation problems, some technologies, and particularly technologies based upon LCDs, display an undesirable characteristic called color divergence and is due to misalignment of the three modulators. Color divergence is essentially having one side of a white pixel one color and the other side another color such as red and blue.
As mentioned, in the previously available devices, it was common to use three light modulating devices, one for each color, and also to use a single light modulating device to display the entire image, or field sequentially, with a single color before switching to the next color. However, the use of three light modulating devices increases the cost, weight, power requirements and complexity of the projection system.
In view of the foregoing, it is noteworthy that none of the known prior art provides a projection system that scans full-color sequentially, column by column. The available art is thus characterized by several disadvantages that are addressed by the present disclosure. The present disclosure minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
The features and advantages of the disclosure will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the disclosure without undue experimentation. The features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.